This application claims the priority of German Application No. 198 37 834.4, filed Aug. 20, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for operationally testing an exhaust gas turbocharger with a variable turbine geometry.
From German Patent document DE 195 43 190 A1, an engine braking system is known for a supercharged internal-combustion engine. The engine has a turbine with a turbine geometry which can be variably adjusted by way of adjustable guide baffles. The guide baffles comprise guide blades, which can be adjusted by means of a control element such that the effective turbine cross-section of the turbine is changed. As a result, it is possible, according to the operating condition of the internal-combustion engine, to implement pressures of different intensities in the section between the cylinders and the exhaust gas turbocharger, whereby the output of the turbine and the output of the compressor can be adjusted according to the requirements.
In order to achieve an engine braking effect in the braking operation of the internal-combustion engine, the guide baffles are changed to a ram position in which the turbine cross-section is clearly reduced. In the section between the cylinders and the exhaust gas turbocharger, a high excess pressure is built up. At the same time, exhaust gas flows at a high flow rate through the ducts between the guide blades and acts upon the turbine wheel, whereby the combustion air supplied to the engine is subjected to excess pressure by the compressor.
As a result, the cylinder is acted upon with increased supercharging pressure on the inlet side. On the outlet side, an excess pressure exists between the cylinder outlet and the exhaust gas turbocharger which counteracts the blowing-off of the air compressed in the cylinder by way of decompression valves into the exhaust gas pipe system. In the engine braking operation, the piston must carry out compression work in the compression and push-out stroke against the high excess pressure in the exhaust gas pipe system, whereby a strong braking effect is achieved.
By way of shut-off bodies, which can be moved into the spaces between the guide blades of the guide baffles, the exhaust gas back pressure between the cylinder outlet and the turbine can be additionally increased in the engine braking operation for increasing the engine braking effect. By way of the shut-off bodies, the effective turbine cross-section is adjusted such that the exhaust gas back pressure required for the desired braking effect is reached in the exhaust gas pipe system.
The shut-off body movement into the spaces between the guide blades is detected by a sensor and analyzed. If faults are recognized in the shut-off body movement, it is attempted to control the effective turbine cross-section only by way of the variable guide baffles without any shut-off bodies. If a fault is also present in the movement of the guide blades of the guide baffles, a fault signal is transmitted to the engine control system and is emitted.
Another method for controlling the supercharging pressure is known from German Patent document DE 195 31 871 C1. In order to permit, by means of simple devices, a control in the transient operation of the internal-combustion engine, particularly after a positive load change from low load and rotational speed ranges, and to improve the efficiency, it is suggested according to this document to determine the difference between the exhaust gas back pressure and the supercharging pressure for the adjustment of the supercharging pressure as the control quantity for the control. As a result, an unacceptably high deviation of the exhaust gas back pressure can be recognized in the case of a positive load change and can be corrected by suitable measures. This control method is used in the fired operation.
From German Patent document DE 27 09 667 C2, an internal-combustion engine with an exhaust gas turbocharger of a conventional construction is known. For monitoring the operating capability of the bypass control in the exhaust gas turbocharger, the supercharging pressure is measured. If the supercharging pressure assumes an unacceptably high value, the inlet collecting pipe of the internal-combustion engine is connected with the atmosphere and the quantity of the fuel to be injected is reduced. Although this makes the turbocharger inoperable, the danger of a component overloading is reduced.
German Patent document DE-OS 23 14 576 discloses a system for detecting faults for an internal-combustion engine. By way of measuring sensors, the load condition, the ambient temperature and the rotational speed of the internal-combustion engine can be determined. When a fault signal occurs in one of the measuring sensors, a monitoring or analysis of structural components or constructional units assigned to the internal-combustion engine can be carried out. However, German Patent document DE-OS 23 14 576 does not discuss the problem of testing the operation of an exhaust gas turbocharger with a variable turbine geometry.
The invention is based on the problem of trying to early diagnose any malfunctioning of exhaust gas turbochargers with a variable turbine geometry.
According to the invention, this problem is solved by the method for operationally testing an exhaust gas turbocharger with a variable turbine geometry for the changeable adjustment of the effective turbine cross-section, in which the actual values of operating quantities influencing the operational capability of the exhaust gas turbocharger are detected which comprise main quantities used for the decision of whether a fault is present in the exhaust gas turbocharger, as well as auxiliary quantities which describe a component of the exhaust gas turbocharger and are used for identifying the fault of this component. In a first step, for the fault detection, a quantity determining the engine air supply is measured as a main quantity. In a second step, at least one auxiliary quantity is measured for the fault identification and, in the event of an unacceptable deviation of the actual auxiliary quantity value from the desired auxiliary quantity value, a fault signal is generated. The position of an adjusting element is measured as an auxiliary quantity, by way of which adjusting element the variable turbine geometry is adjustable.
During the operational testing, two types of operating quantities are determined, which each describe the performance of the exhaust gas turbocharger but which have different functions: Main quantities, which are a measurement of the basic operability of the exhaust gas turbocharger and to which a value is assigned to determine the engine air supply, as well as auxiliary quantities from which a conclusion can be drawn on the operability of a certain component. The auxiliary quantities depend on the construction of the exhaust gas turbocharger. They expediently indicate the position of an adjusting element of the variable turbine geometry.
In a first step of the operational testing of the turbocharger, a main quantity is measured first and is used as a basis for deciding whether there is a malfunctioning. The main quantity forms the decision basis for the fault detection.
If a fault is present, the auxiliary quantity is measured in a second step and is used for the fault identification. The value of the auxiliary quantity is a measurement of the operating capability of the variable turbine geometry. In the event of a fault, the value of the auxiliary quantity is outside the permissible range; the concerned component is inoperable or its operability is limited.
The fault detection by way of the main quantity determining the engine air supply has the advantage that, as a rule, several measuring devices can be used which already exist and which are required for the control in the fired operation and in the engine braking operating, whereby no additional expenditures are caused for the sensor system.
Another advantage is the two-step characteristic of the method for operational testing, whereby the sum of data is reduced which have to be measured and analyzed. The basic decision of whether the exhaust gas turbocharger is inoperable can be made only by the comparison of the measuring data representing the engine air supply with the pertaining desired values. In this stage, it is not absolutely necessary to measure the auxiliary quantities, which supply information on the operating capability of a certain component. The measuring of the auxiliary quantities only becomes necessary if the analysis of the main quantity points to a fault in the exhaust gas turbocharger. The two-step characteristic of the method permits the obtaining of information concerning the operability on the basis of a minimal data base.
By means of the two-step method, the smallest deviations of the charge pressure from the desired value can be recognized and the fault can be assigned to a specific component. A charge pressure which is too low and which negatively influences the braking performance in the engine braking operation and the engine performance in the fired operation, as well as an excessive supercharging pressure, which may lead to an overloading of the exhaust-gas-carrying and supercharging-air-carrying systems, can be recognized on the basis of this method.
All condition quantities and operational quantities of the exhaust gas turbocharger can be used as main quantities which represent a measurement of the engine air supply. This can be detected by a direct measurement by way of the air flow to the engine as well as by an indirect measurement by way of the supercharging pressure, the rotational engine speed and the temperature.
The operational testing can be continuously carried out, specifically in the fired operation as well as in the engine braking operation. In the engine braking operation, the supercharging pressure and the rotational engine speed are preferably taken into account as the main quantities; in the fired operation, the engine load is preferably also taken into account.
In addition, the time from the start of the engine braking operation or of the fired operation is measured in order to take into account dynamic influences on the main quantities and auxiliary quantities and in order to be able to detect the transient performance of the exhaust gas turbocharger.
By way of the determination of the momentary point in time at which a measurement is carried out, dynamic transient effects can be taken into account in the desired-actual comparison between measured values and defined desired values.
As the auxiliary quantity, the position of the adjusting element is detected, which is part of the variable turbine geometry and by way of which the effective turbine cross-section can be adjusted. According to the construction of the used exhaust gas turbocharger, axially displaceable turbine guide baffles can be used as an adjusting element, and the end positions of the guide baffles can be used as the auxiliary quantity, or, guide baffles with rotary blades can be used as the adjusting element and the rotary position of the rotary blades can be used as the auxiliary quantity. As another turbine type, a turbine with a braking flap disposed in front of it can be used, as the auxiliary quantity, the actual position of the braking flap being taken into account.
Optionally, several main quantities and/or auxiliary quantities can be taken into account. The blow-off cross-section of a blow-off or brake valve can be used as additional auxiliary quantities, or parameters which allow conclusions with respect leakages in the supercharging-air guiding / exhaust gas guiding or other damage in the area of the exhaust gas turbocharger.
The operational testing expediently takes place at regular time intervals, whereby the operational reliability is increased and, in addition, information can be obtained concerning the time-related development of the operability of individual components.